/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory.config;

import kotlin.reflect.KProperty;
import kotlin.reflect.jvm.ReflectJvmMapping;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.InjectionPoint;
import org.springframework.beans.factory.NoUniqueBeanDefinitionException;
import org.springframework.core.KotlinDetector;
import org.springframework.core.MethodParameter;
import org.springframework.core.ParameterNameDiscoverer;
import org.springframework.core.ResolvableType;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.lang.Nullable;
import org.springframework.util.ObjectUtils;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.Map;
import java.util.Optional;

/**
 * Descriptor for a specific dependency that is about to be injected.
 * Wraps a constructor parameter, a method parameter or a field,
 * allowing unified access to their metadata.
 *
 * @author Juergen Hoeller
 * @since 2.5
 */
@SuppressWarnings("serial")
public class DependencyDescriptor extends InjectionPoint implements Serializable {
    // A里面注入了B，则声明类是 A
    private final Class<?> declaringClass;

    @Nullable
    private String methodName;

    @Nullable
    private Class<?>[] parameterTypes;

    private int parameterIndex;

    @Nullable
    private String fieldName;

    private final boolean required;
    // 饥饿的，非懒加载的
    private final boolean eager;

    private int nestingLevel = 1;
    // 代理类
    @Nullable
    private Class<?> containingClass;

    @Nullable
    private transient volatile ResolvableType resolvableType;

    @Nullable
    private transient volatile TypeDescriptor typeDescriptor;


    /**
     * Create a new descriptor for a method or constructor parameter.
     * Considers the dependency as 'eager'.
     * @param methodParameter the MethodParameter to wrap
     * @param required whether the dependency is required
     */
    public DependencyDescriptor(MethodParameter methodParameter, boolean required) {
        this(methodParameter, required, true);
    }

    /**
     * Create a new descriptor for a method or constructor parameter.
     * @param methodParameter the MethodParameter to wrap
     * @param required whether the dependency is required
     * @param eager whether this dependency is 'eager' in the sense of
     * eagerly resolving potential target beans for type matching
     */
    public DependencyDescriptor(MethodParameter methodParameter, boolean required, boolean eager) {
        super(methodParameter);

        this.declaringClass = methodParameter.getDeclaringClass();
        if (methodParameter.getMethod() != null) {
            this.methodName = methodParameter.getMethod().getName();
        }
        this.parameterTypes = methodParameter.getExecutable().getParameterTypes();
        this.parameterIndex = methodParameter.getParameterIndex();
        this.containingClass = methodParameter.getContainingClass();
        this.required = required;
        this.eager = eager;
    }

    /**
     * Create a new descriptor for a field.
     * Considers the dependency as 'eager'.
     * @param field the field to wrap
     * @param required whether the dependency is required
     */
    public DependencyDescriptor(Field field, boolean required) {
        this(field, required, true);
    }

    /**
     * Create a new descriptor for a field.
     * @param field the field to wrap
     * @param required whether the dependency is required
     * @param eager whether this dependency is 'eager' in the sense of
     * eagerly resolving potential target beans for type matching
     */
    public DependencyDescriptor(Field field, boolean required, boolean eager) {
        super(field);

        this.declaringClass = field.getDeclaringClass();
        this.fieldName = field.getName();
        this.required = required;
        this.eager = eager;
    }

    /**
     * Copy constructor.
     * @param original the original descriptor to create a copy from
     */
    public DependencyDescriptor(DependencyDescriptor original) {
        super(original);

        this.declaringClass = original.declaringClass;
        this.methodName = original.methodName;
        this.parameterTypes = original.parameterTypes;
        this.parameterIndex = original.parameterIndex;
        this.fieldName = original.fieldName;
        this.containingClass = original.containingClass;
        this.required = original.required;
        this.eager = original.eager;
        this.nestingLevel = original.nestingLevel;
    }


    /**
     * Return whether this dependency is required.
     * <p>Optional semantics are derived from Java 8's {@link java.util.Optional},
     * any variant of a parameter-level {@code Nullable} annotation (such as from
     * JSR-305 or the FindBugs set of annotations), or a language-level nullable
     * type declaration in Kotlin.
     */
    public boolean isRequired() {
        if (!this.required) {
            return false;
        }

        if (this.field != null) {
            return !(this.field.getType() == Optional.class || hasNullableAnnotation() ||
                    (KotlinDetector.isKotlinReflectPresent() &&
                            KotlinDetector.isKotlinType(this.field.getDeclaringClass()) &&
                            KotlinDelegate.isNullable(this.field)));
        }
        else {
            return !obtainMethodParameter().isOptional();
        }
    }

    /**
     * Check whether the underlying field is annotated with any variant of a
     * {@code Nullable} annotation, e.g. {@code javax.annotation.Nullable} or
     * {@code edu.umd.cs.findbugs.annotations.Nullable}.
     */
    private boolean hasNullableAnnotation() {
        for (Annotation ann : getAnnotations()) {
            if ("Nullable".equals(ann.annotationType().getSimpleName())) {
                return true;
            }
        }
        return false;
    }

    /**
     * Return whether this dependency is 'eager' in the sense of
     * eagerly resolving potential target beans for type matching.
     */
    public boolean isEager() {
        return this.eager;
    }

    /**
     * Resolve the specified not-unique scenario: by default,
     * throwing a {@link NoUniqueBeanDefinitionException}.
     * <p>Subclasses may override this to select one of the instances or
     * to opt out with no result at all through returning {@code null}.
     * @param type the requested bean type
     * @param matchingBeans a map of bean names and corresponding bean
     * instances which have been pre-selected for the given type
     * (qualifiers etc already applied)
     * @return a bean instance to proceed with, or {@code null} for none
     * @throws BeansException in case of the not-unique scenario being fatal
     * @since 5.1
     */
    @Nullable
    public Object resolveNotUnique(ResolvableType type, Map<String, Object> matchingBeans) throws BeansException {
        throw new NoUniqueBeanDefinitionException(type, matchingBeans.keySet());
    }

    /**
     * Resolve the specified not-unique scenario: by default,
     * throwing a {@link NoUniqueBeanDefinitionException}.
     * <p>Subclasses may override this to select one of the instances or
     * to opt out with no result at all through returning {@code null}.
     * @param type the requested bean type
     * @param matchingBeans a map of bean names and corresponding bean
     * instances which have been pre-selected for the given type
     * (qualifiers etc already applied)
     * @return a bean instance to proceed with, or {@code null} for none
     * @throws BeansException in case of the not-unique scenario being fatal
     * @since 4.3
     * @deprecated as of 5.1, in favor of {@link #resolveNotUnique(ResolvableType, Map)}
     */
    @Deprecated
    @Nullable
    public Object resolveNotUnique(Class<?> type, Map<String, Object> matchingBeans) throws BeansException {
        throw new NoUniqueBeanDefinitionException(type, matchingBeans.keySet());
    }

    /**
     * Resolve a shortcut for this dependency against the given factory, for example
     * taking some pre-resolved information into account.
     * <p>The resolution algorithm will first attempt to resolve a shortcut through this
     * method before going into the regular type matching algorithm across all beans.
     * Subclasses may override this method to improve resolution performance based on
     * pre-cached information while still receiving {@link InjectionPoint} exposure etc.
     * @param beanFactory the associated factory
     * @return the shortcut result if any, or {@code null} if none
     * @throws BeansException if the shortcut could not be obtained
     * @since 4.3.1
     */
    @Nullable
    public Object resolveShortcut(BeanFactory beanFactory) throws BeansException {
        return null;
    }

    /**
     * Resolve the specified bean name, as a candidate result of the matching
     * algorithm for this dependency, to a bean instance from the given factory.
     * <p>The default implementation calls {@link BeanFactory#getBean(String)}.
     * Subclasses may provide additional arguments or other customizations.
     * @param beanName the bean name, as a candidate result for this dependency
     * @param requiredType the expected type of the bean (as an assertion)
     * @param beanFactory the associated factory
     * @return the bean instance (never {@code null})
     * @throws BeansException if the bean could not be obtained
     * @since 4.3.2
     * @see BeanFactory#getBean(String)
     */
    public Object resolveCandidate(String beanName, Class<?> requiredType, BeanFactory beanFactory)
            throws BeansException {

        return beanFactory.getBean(beanName);
    }


    /**
     * Increase this descriptor's nesting level.
     */
    public void increaseNestingLevel() {
        this.nestingLevel++;
        this.resolvableType = null;
        if (this.methodParameter != null) {
            this.methodParameter = this.methodParameter.nested();
        }
    }

    /**
     * Optionally set the concrete class that contains this dependency.
     * This may differ from the class that declares the parameter/field in that
     * it may be a subclass thereof, potentially substituting type variables.
     * @since 4.0
     */
    public void setContainingClass(Class<?> containingClass) {
        this.containingClass = containingClass;
        this.resolvableType = null;
        if (this.methodParameter != null) {
            this.methodParameter = this.methodParameter.withContainingClass(containingClass);
        }
    }

    /**
     * Build a {@link ResolvableType} object for the wrapped parameter/field.
     * @since 4.0
     */
    public ResolvableType getResolvableType() {
        ResolvableType resolvableType = this.resolvableType;
        if (resolvableType == null) {
            resolvableType = (this.field != null ?
                    ResolvableType.forField(this.field, this.nestingLevel, this.containingClass) :
                    ResolvableType.forMethodParameter(obtainMethodParameter()));
            this.resolvableType = resolvableType;
        }
        return resolvableType;
    }

    /**
     * Build a {@link TypeDescriptor} object for the wrapped parameter/field.
     * @since 5.1.4
     */
    public TypeDescriptor getTypeDescriptor() {
        TypeDescriptor typeDescriptor = this.typeDescriptor;
        if (typeDescriptor == null) {
            typeDescriptor = (this.field != null ?
                    new TypeDescriptor(getResolvableType(), getDependencyType(), getAnnotations()) :
                    new TypeDescriptor(obtainMethodParameter()));
            this.typeDescriptor = typeDescriptor;
        }
        return typeDescriptor;
    }

    /**
     * Return whether a fallback match is allowed.
     * <p>This is {@code false} by default but may be overridden to return {@code true} in order
     * to suggest to an {@link org.springframework.beans.factory.support.AutowireCandidateResolver}
     * that a fallback match is acceptable as well.
     * @since 4.0
     */
    public boolean fallbackMatchAllowed() {
        return false;
    }

    /**
     * Return a variant of this descriptor that is intended for a fallback match.
     * @since 4.0
     * @see #fallbackMatchAllowed()
     */
    public DependencyDescriptor forFallbackMatch() {
        return new DependencyDescriptor(this) {
            @Override
            public boolean fallbackMatchAllowed() {
                return true;
            }
        };
    }

    /**
     * Initialize parameter name discovery for the underlying method parameter, if any.
     * <p>This method does not actually try to retrieve the parameter name at
     * this point; it just allows discovery to happen when the application calls
     * {@link #getDependencyName()} (if ever).
     */
    public void initParameterNameDiscovery(@Nullable ParameterNameDiscoverer parameterNameDiscoverer) {
        if (this.methodParameter != null) {
            this.methodParameter.initParameterNameDiscovery(parameterNameDiscoverer);
        }
    }

    /**
     * Determine the name of the wrapped parameter/field.
     * @return the declared name (never {@code null})
     */
    @Nullable
    public String getDependencyName() {
        return (this.field != null ? this.field.getName() : obtainMethodParameter().getParameterName());
    }

    /**
     * Determine the declared (non-generic) type of the wrapped parameter/field.
     * @return the declared type (never {@code null})
     */
    public Class<?> getDependencyType() {
        if (this.field != null) {
            if (this.nestingLevel > 1) {
                Type type = this.field.getGenericType();
                for (int i = 2; i <= this.nestingLevel; i++) {
                    if (type instanceof ParameterizedType) {
                        Type[] args = ((ParameterizedType) type).getActualTypeArguments();
                        type = args[args.length - 1];
                    }
                }
                if (type instanceof Class) {
                    return (Class<?>) type;
                }
                else if (type instanceof ParameterizedType) {
                    Type arg = ((ParameterizedType) type).getRawType();
                    if (arg instanceof Class) {
                        return (Class<?>) arg;
                    }
                }
                return Object.class;
            }
            else {
                return this.field.getType();
            }
        }
        else {
            return obtainMethodParameter().getNestedParameterType();
        }
    }


    @Override
    public boolean equals(@Nullable Object other) {
        if (this == other) {
            return true;
        }
        if (!super.equals(other)) {
            return false;
        }
        DependencyDescriptor otherDesc = (DependencyDescriptor) other;
        return (this.required == otherDesc.required && this.eager == otherDesc.eager &&
                this.nestingLevel == otherDesc.nestingLevel && this.containingClass == otherDesc.containingClass);
    }

    @Override
    public int hashCode() {
        return (31 * super.hashCode() + ObjectUtils.nullSafeHashCode(this.containingClass));
    }


    //---------------------------------------------------------------------
    // Serialization support
    //---------------------------------------------------------------------

    private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
        // Rely on default serialization; just initialize state after deserialization.
        ois.defaultReadObject();

        // Restore reflective handles (which are unfortunately not serializable)
        try {
            if (this.fieldName != null) {
                this.field = this.declaringClass.getDeclaredField(this.fieldName);
            }
            else {
                if (this.methodName != null) {
                    this.methodParameter = new MethodParameter(
                            this.declaringClass.getDeclaredMethod(this.methodName, this.parameterTypes), this.parameterIndex);
                }
                else {
                    this.methodParameter = new MethodParameter(
                            this.declaringClass.getDeclaredConstructor(this.parameterTypes), this.parameterIndex);
                }
                for (int i = 1; i < this.nestingLevel; i++) {
                    this.methodParameter = this.methodParameter.nested();
                }
            }
        }
        catch (Throwable ex) {
            throw new IllegalStateException("Could not find original class structure", ex);
        }
    }


    /**
     * Inner class to avoid a hard dependency on Kotlin at runtime.
     */
    private static class KotlinDelegate {

        /**
         * Check whether the specified {@link Field} represents a nullable Kotlin type or not.
         */
        public static boolean isNullable(Field field) {
            KProperty<?> property = ReflectJvmMapping.getKotlinProperty(field);
            return (property != null && property.getReturnType().isMarkedNullable());
        }
    }

}
